Blank holder circuit with automatic release of blank holder pressure on idle stroke



Aug. 19, 1941. w ERNST 2,252,881 BLANK HOLDER CIRCUIT WITH AUTOMATIC RELEASE OF BLANK HOLDER PRESSURE ON IDLE STROKE Filed March 27, 1939 2 Sheats-Sheet 1 Im/zntor WALTER E RNT by QKMJI 'W T 5% Attdmzys Aug. '19, 1941.

w. ERNST 2,252,881 BLANK HOLDER CIRCUIT WITH AUTOMATIC RELEASE OF BLANK HOLDER PRESSURE 0N IDLE STROKE Filed March 27, 1939 2 Sheets- Sheet 2 Patented Aug. 19, 1941 BLANK HOLDER CIRC RELEASE OF BLAN ON IDLE STROKE UIT WITH AUTOMATIC K HOLDER PRESSURE Walter Ernst, Mount Gilead, Ohio, assignor to The Hydraulic Development Corp. Inc., Wilmington, Del., a corporation of Delaware Application March 27, 1939, Serial No. 264,311

Claims.

This invention relates to presses, and in particular, to hydraulic presses having clamping mechanism associated with drawing mechanism.

One object of this invention is to provide a hydraulic press having a drawing plunger and a clamping plunger, means being provided for releasing the pressure from the clamping plunger during the retraction stroke of the drawing plunger, together with means for preventing the release of this pressure during the drawing stroke.

Another object is to provide a hydraulic press having a drawing plunger and a clamping plunger, together with means responsive to the reversal of pressure fluid for retracting the drawing plunger in order to release the pressure in the clamping plunger.

Another object is to provide a hydraulic press having a drawing plunger and a clamping plunger, tog-ether with a valve shifted in response to the reversal of the drawing plunger by pressure fluid supplied for retracting the latter so that the valve for releasing the pressure from the clamping plunger is automatically actuated by the pressure condition existing in the drawing plunger circuit without the necessity for the provision of linkages or other mechanism interconnecting the drawing plunger with the valve.

Another object is to provide a. method of producing drawn articles, residing in clamping the article, at its periphery by hydraulically operated means while performing the drawing operation, and thereafter releasing the pressure from the hydraulic clamping means in response to the reception of pressure for reversing the drawing operation.

In the drawings: 1

Figure 1 is a diagrammatic view, partly in section, showing the working elements of a hydraulic drawing press circuit according to one embodiment of this invention, wherein a reversing valve controls the distribution of fluid to the drawing plunger.

Figure 2 is a diagrammatic view of a modification of the circuit shown in Figure 1, wherein a reversible pump is employed for reversely distributing pressure fluid to the drawing plunger to advance and retract the latter.

General arrangement In general, the drawing press of this invention consists of a drawing plunger and a plurality of clamping plungers having relief valves associated therewith for release of the pressure fluid therein at predetermined pressures, thereby enabling a predetermined clamping pressure to be exerted on the blank. The relief valves may be set at dii ferent loadings so as to provide different clamping pressures at different points upon the blank. Check valves are employed to prevent the interflow of fluid between the various clamping cylinders, thereby preventing equalization of clamping pressures. The hydraulic circuit also includes a two-way valve connected to the clamping cylinders, and operated in response to the admission of pressure fluid into the retraction circuit of the drawing plunger. By'this arrangement it is impossible to release the clamping pressure until the retraction stroke'of the drawing plunger has been started.

Hitherto, the provision of a platen-operated valve for releasing the pressure from the clampin cylinders has required complex mechanism, such as linkages actuated by the platen for shifting the valve. This, in turn, has required an individual adjustment of this mechanism to be made every time the dies are changed, and has always created the danger of erroneous adjustment whereby the valve would not be operated at all, or would be operated at the wrong position. According to the present invention, however, the platen-operated mechanism for shifting the valve is entirely eliminated, and instead the valve is shifted by pressure fluid applied thereto when pressure fluid is admitted into the retraction circuit of the drawing plunger. This construction simplifies the external appearance of the press, results in economy of manufacture, avoids the possibility of maladjustment and saves the time hitherto required for adjusting the platen-operated mechanism to suit various dies. According to the present invention also the clamping pressure releasing valve is preferably mounted inside the oil reservoir so that leakage is of no consequence.

Press circuit employing pump with reversing valve die I is received within a bore I! in the base member H). The drawing press of the present invention may utilize either flat blanks or blanks which have already been subjected to one or more drawing operations. In Figures 1 and 2 the blank passages Also associated with the top member Ill is a main cylinder or drawing cylinder 28, having a bore 2| reciprocably receiving the double-acting main plunger or drawing plunger 22 having a piston head 23 thereon. The cylinder 28 is provided with upper and lower ports 24 and 25 on opposite sides of the piston head 23, and adapted by means of pipes 26 and 21 to supply pressure fluid to advance or retract the drawing plunger 22. The delivery of pressure fluid to the main cylinder 28 and the exhaustion of fluid therefrom are controlled by a four-way valve 28. This valve 28 is of any suitable type known to those skilled in the art, and its details form no part of the present invention.

Leading to the four-way valve 28 is a pressure line 29, connected at its opposite end to a hydraulic pump 38. An exhaust line 3| leads from the four-way valve 28 to the interior of the surge tank IS. The pump 38 is also provided with a suction line 32, likewise leading into the interior of the surge tank IQ for, supplying fluid to the pump. The main or drawing cylinder 28 is provided, near its lower end, with a packing ring 33 having a packing 34 associated therewith and adapted to be compressed by a gland 35 in such a manner as to prevent leakage around the drawing plunger 22.

Mounted upon the lower end of the drawing plunger 22 is a platen 36 containing clamping cylinders 31, having clamping plungers 38 reciprocable therein. Each clamping cylinder 31 is provided with a packing 39 surrounding the clamping plunger 38, and compressedby a gland 48 for the preventionof leakage. Mounted upon the platen 36 is a drawing die member or punch 4|, cooperating with the drawing die I4 and having a nose portion 42 approximately corresponding to the die cavity I5. The punch 4| is adapted to pass through an aperture 43 in a clamping ends of the clamping plungers 38.

The clamping cylinders '31 are provided with 41 connected to the bores 49 of tubular plungers 48, mounted upon the upper side of the platen 36. The hollow plungers 46 pass through glands 58 and packings 5|, into cylinders 52 ar ranged on the press top member H and within the surge tank I9. From each cylinder 52 the line 53 leads through the check valve 54 to the interior of the surge tank I9. Each check valve 54 opens in the direction of the cylinder 52 so that the latter may draw in fluid upon the descent of the hollow plungers 48. The check valves 54, however, close and. prevent the discharge of fluid upon the ascent of the plungers 48.

From each cylinder 52 a T-shaped line 55 leads also to a safety valve 56 and a pressure relief valve 51. The safety valve 56 is merely provided as an additional safety feature in the event of a jamming or other failure of the safety valve 51. The safety valve 56, however, is set to release pressure at a higher pressure than the safety valve 51, hence, does not become operative unless the safety valve 51 fails to release fluid in response to the accumulation of a dangerous pressure witl in the corresponding clamping member 44, the latter being secured to the outer cylinder 31. Each clamping cylinder 31 is provided with its own pressure relief valve 51 and safety valve 56 so that a difierent pressure release point may be provided for each clamping cylinder 31, if desired. This, in turn, enables different clamping pressures to be exerted upon different portions of the periphery of the blank l6, a feature which is useful in certain classes of drawing work.

The valves 56 and 51 both discharge into the discharge line 58, leading to the interior of the surge tank I9. A pressure gauge 59 is connected to each line 55 to indicate pressure existing in the associated clamping cylinder 31. Extending from each clamping cylinder 52 is a line 6| having therein a check valve 62, opening in a direction awayfrom its associated clamping cylinder 52 and toward a common line 63 connected thereto. The line 63 leads to a two-way valve 18, having a cylindrical bore 1| containing a valve member 12 with valve heads 13 and 14. The opposite ends of the cylinder bore 1| are provided with ports 15 and 16. A branch line 11 leads from the line 26 to the port 16, whereas a branch line 18 leads from the line 21 to the port 15. The cylinder bore 1| likewise contains a discharge port 19, opening directly into the interior of the surge tank l9, and an additional port 88 to which the line 63 is connected. The end portions of the valve bore 1| immediately adjacent the ports 15 and 16 serve as pilot chambers or valve-actuating chambers for shifting the valve member 12 in response to the reception of pressure fluid either along the line 18 or 11 from the line 21 or 28, respectively. j

The platen 36 is provided with bores 8| adapted to receive rods 82, the lower ends of which are secured to the clamping platen 44 and the upper ends of which are externally threaded, as at 88,

and provided with nuts 84 threaded thereon.

The upper ends of the rods 82 are likewiseprovided with internal threaded bores 85, carrying the threaded rods 86. This construction provides means for stripping the workpiece from the punch 4| when the rods 86 encounter the press top member upon the return stroke of the main plunger 22. The construction permits this ejection 0r knock-out point to be accurately adjusted for each different type of workpiece.

Operation line 26, and thence to the upper part of the main cylinder 28 above the piston head 23. At the same time fluid is exhausted from beneath the piston head 23, through the line 21, and is discharged through the valve 28 to the line 3|, and thence into the surge tank l9. When this occurs pressure fluid likewise passes through the line 11 and port 16, into the left-hand end of the cylinder bore 1|, any fluid in the right-hand end of the cylinder bore 1| being discharged through the port 15 and line 18 by way of the valve 28 and line 3|, into the surge tank l3.

Under the influence of the pressure in the line 11 the valve member 12 is pushed to the right so that the valve head 13 comes to rest between the ports 88 and 18. Under these conditions liquid is trapped in the left-hand end of the cylinder bore 1|, and cannot escape through the port 19. Ordinarily, a surge valve is provided in the top of the main cylinder 28 to admit fluid freely upon the downward stroke of the drawing plunger 22, thereby accelerating the gravitational descent of the platen 36. This surge valve is omitted for simplicity of disclosure, and its use is well known to those skilled in the art.

As the main plunger 22 moves downward it carries with it the platen 36 and the clamping assembly, which includes the clamping platen 44, the clamping plungers 38 and the tubular plungers 48. The suction thereby created in the cylinders 52 opens the check valves 54 and causes fluid to be drawn from the surge tank I8, into the cylinders 52. When the clamping member or clamping platen 44 has descended to a point where it engages the workpiece I6 it halts. The platen 38, however, continues to advance and moves the punch into engagement with the workpiece I6. By reason of the relative motion thus created between the halted clamping plungers 38 and the moving clamping cylinders 37, fluid is displaced by the plungers 38 from the cylinders 31. The displaced fluid passes through the bores 48, into the cylinders 52. As the cross sectional area of the clamping plungers 38 is greater than the cross sectional area of the tubular plungers 48, however, more fluid is discharged from the clamping cylinders 31 into the cylinders 52 than there is room for. This results in pressure being built up in the cylinders 31 and 52, and this pressure acts against the heads of the plungers 48 and 38 to force the clamping member or clamping platen 44 firmly into engagement with the periphery of the workpiece I6.

When pressure in this clamping system exceeds the setting of the relief valves 51, the latter open and permit the excess fluid to be discharged through the lines 58, into the surge tank I9. The check valves 54 prevent the escape of fluid through the lines 53, and the closed position of the valve I8 prevents the discharge of fluid from the line 63 since the valve head 13 now stands between the ports 88 and I8. Consequently, the

clamping platen 44 grips the periphery of the workpiece or blank l6 while the punch 4| is urged downward by the main platen 36, thereby performing the drawing operation upon the workpiece I6. When the required operation has been completed, the valve lever 8'! is manipulated to shift the four-way valve 28 so that pressure fluid is discharged from the pump 38, into the line 21 leading to the retraction side of the main plunger 22. At the same time the space above the piston head 23 is open to exhaust through the line 26, the four-way valve 28 and the exhaust line 3| leading to the surge tank I8. Under these conditions the main plunger 22 and main platen 36 move upward.

The admission of pressure fluid to the retraction line 21 also admits pressure fluid to the line I8, this fluid entering the port I at the righthandend of the cylinder bore 'II in the valve 18, and shifts the valve member 12 to the left into the position shown in Figure 1. As the tubular plungers 48 move upward, therefore, the fluid displaced from the cylinders 52 escapes through the lines 5|, the check valves 52, the line 53, the port 88, the valve bore II and the port I9, into the surge tank I9. This enables the tubular plungers 48 to be freely retracted along with the main plunger 22 and main platen 26. In the arrangement of Figure 1, therefore, the valve I8 is automatically shifted to permit the escape of fluid from the cylinders 52 the instant that pressure fluid is admitted to the retraction side of the main plunger 22. Ther is thus no necessity 75 pivotally connected at its for any leakage or any attention on the part of the operator for shifting the valve I8 to permit the escape of this fluid.

Modified drawing press circuit employing reversible pump is provided with a valve bore 9|, containing a valve member 92 having heads 93 and 84. The valve member 92 carries a third valve head 85, reciprocable in an independent bore 88, having ports 91 and 98 at the opposite ends thereof. The valve bore 9| is provided with ports 99 and I88, similar in arrangement and purpose to the ports I9 and 88 of the valve I8 in Figure 1. The line 63 is connected, in Figure 2, to the port I88 and the port 99 opens directly into the interior of the surge tank I9. I

In the circuit of Figure .2 the pressure fluid is supplied selectively to the 1ine,2| or 28 from a reversible variable delivery pump IN. The latter is provided with a flow-control member or shift ring (not shown), familiar to those skilled in the art, and shifted to and fro by a servomotor I82 in order to vary the direction and amount of the fluid delivered from the pump I8I. Mounted on the opposite side of the pump I 8| from the servo-motor I82 is a safety centering device I83 for shifting the flow-control member of the pump I8I to its neutral position in the event of a power failure to t e motor driving the pump IIII. The details of theservomotor I82 and safety centering device I83 form no part of the present invention, and are disclosed in the copending application of Walter Ernst, Ser. No. 170,250, filed October 21, 1937.

The servomotor I82 contains a servopiston connected to the pump flow-control member, and actuated in opposite directions in response to the shiftingof the servomotor control valve member I84. The latter is pivotally connected to a lever I85 mounted upon a floating link I88, and opposite end to a link I87, which is pivotally connected to a lever I88 mounted upon a fixed fulcrum I89, secured to a bracket 8 mounted upon the press head II, or any stationary part of the press. The lower end of the lever I88 is pivotally connected to a link III, the opposite end of which is pivotally connected to an arm a rocker arm H3.

The rocker arm H3 i pivotally mounted upon a fulcrum I 14, supported upon the press head II, or any other stationary part of the press. One end of the rocker arm II3 is provided with a. rounded yoke portion II5 engaging a collar H8 upon the press control rod 1. The latter is reciprocably supported upon the press, such as in the bore II8 on the press head I I, and by the bore II 9 in the bracket I28 secured to the press bed I 8.

The platen 36 carries a platen arm I2I engageable with an adjustable collar I22 upon the control rod Ill. The opposite end of the rocker arm II3 from the yoke portion H5 is pivotally connected to a rod I23, leading to the armature I 24 01' a solenoid I25. The energization of -the solenoid I25, acting through the above-mentioned II2 operatively connected to inder 20.

linkage, pushes the servomotor control valve member I04 to the right, whereas a spring within the servomotor I02 urges it to the left when the solenoid I25 is deenergized. When the platen 36 reaches its retracted position, the arm I2I lifts the 'control rod H1, and the collar II6 thereon shifts the rocker arm I I3 in such a manner as to move the servomotor control valve member I 04 to the right into its neutral' position, thereby placing the flow-control member of the pump ID! in its neutral position, and reducing the delivery of the pump IOI to zero. This halts the platen 36 in its retracted position.

The motor which drives the variable delivery pump IOI also drives a pilot pump I26, preferably from the same shaft. The pilot pump I26 delivers pressure fluid through the line I21 to the servomotor I02, thereby operating the servomotor, and Withdraws fluid from the surge tank I9 by way of the suction line I28. The line I21 thus serves as a pilot pressure line, and contains a relief valve I29 having a discharge line I30 discharging into the surge tank I9. The servomotor I02 is also provided with an exhaust line I3I, similarly discharging into the surge tank IS. A pressure line I32 leads from the servomotor I02 to the end port 91 of the bore 96 within the valve 90. The main cylinder 20 is provided with a bore I33 in the head thereof, and serves to receive a surge valve I34 connected by the line I35 to the line I36, which in turn, is connected to the line 21 leading to the retraction side of the main plunger 22. The surge valve I34 is of the type disclosed in the patent to Walter Ernst, No. 1,892,568, issued December 27, 1932.

The line I36 is provided with a branch line I31 having a check valve I38, opening toward the line I36. The line I36 is additionally provided with a pressure relief valve I39, and is connected at its end to a main cylinder release and by-pass valve I40, having a line IQI leading to the port I42 in the head of the main cyl- A branch line I43 likewise leads from the valve I to the line MI, and a second branch line I44 terminates in a pressure relief valve I45. The details of the main cylinder release and bypass valve I40 form no part of the present invention, and are disclosed in the patent to Walter Ernst, No. 1,956,758, issued May 1, 1934.

Running from the line I36 is a branch line I46 leading to the port 98 in the valve 90.

In order to provide a variable pressure control to alter the encrgization of the solenoid I25 and to automatically reverse the main plunger 22 at the attainment of a predetermined-pressure during its working stroke, there is provided a tonnage control device I41 having a line I48 connected to the port I49 in the head of the main cylinder 20, and likewise having an exhaust line I50 connected to the interior of the surge tank I9. The tonnage control device I41 consists of a spring-loaded hydraulic plunger reciprocable in a chamber connected to the line I48, and movable to actuate an electric witch in circuit with the solenoid I25 when the pressure in the line I48 overcomes the force of .the loading spring, at which time the plunger uncovers a port leading to the line I50, and the excess pressure fluid discharges into the line I50. The loading of the spring within the tonnage control device I41 is regulated by the hand wheel I5I so as to vary the. pressure at which the switch therein becomes operative to alter the energize.- tion of the solenoid I25. The tonnage control device I41 is therefore, in principle, a pressureresponsive electric switch, and its details are well known to those skilled in the art and form no part of the present invention.

Operation of modified press circuit to discharge pressure fluid into the line 26 while withdrawing pressure fluid from the line 21. The main plunger 22 descends, as described in connection with Figure 1, and its gravitational descent is accelerated by the free admission of fluid from the surge tank I9, through the surge valve I34, into the upper end of the main cylinder 20.

At the same time, when the pilot pump I26 delivers pressure fluid to the servomotor I02 to place the pump IOI upon stroke to deliver pressure fluid into the line 26 and advance the main plunger 22, pilot pressure fluid also passes out of the servomotor I02, through the line I32, into the end chamber 96 of the valve 90, acting against the valve head 95 and shifting it to the left. This action, shifts the valve head 94 into a position between the ports I60 and 99, and blocks the escape 'of fluid from the line 63, through the valve 90. Since the pilot pressure fluid remains at practically constant pressure, it can be depended upon to hold the valve in its closed position during the power or working stroke of the main plunger 22. The valve 90 in Figure 2 is operated by pilot pressure in this manner rather than connected to the line 26 leading to the upper end of the main cylinder 20, as is the valve 10 in Figure 1. In this way it is always assured that the valve 90 is operated so as to entrap the fluid in the clamping cylinders prior to the engagement of the workpiece by the clamping members. Although the embodiment of Figure 1 works satisfactorily, it will be appreciated that, because the main plunger 22 descends under the influence of gravity with the aid of the surge valve on top of the main cylinder 20, it may sometimes occur that the necessary pressure for operating the valve 10 is only established after the workpiece I6 has been engaged by the clamping member 44. Thus, the valve might be closed too late to prevent loss of pressure from the cylinders 52 and 31. After the clamping member 44 engages the workpiece I6, the operation of the clamping apparatus 38, 31, 48, 52, etc. is as described in connection with the circuit of Figure 1. When the drawing operation has proceeded to a point where the tonnage control device I41 deenergizes the solenoid I25 to reverse the delivery of the pump ml, the latter then discharges pressure fluid into the retraction line 21 and withdraws fluid from the advancing line 26. The

main plunger 22 then rises, but a portion of the pressure passes through the lines I36 and I46, into the left-hand end of the valve bore 96. This pressure forces the valve head and the valve member 92 to the right, into the position shown in Figure 2. At this time the line I32 is connected to the servomotor exhaust line I3I, and releases any fluid in the right-hand end of the valve bore 96. The consequent shifting of the valve head 94 to the position shown in Figure 2 opens communicatipn between the ports 89 and H10, and permits fluid to escape from the cylindei's 52 and 31 of the clamping circuit analogous to the manner described in connection with Figure 1. The clamping platen 44 is, therefore, permitted to be retracted along with the main plate 36 and main plunger 22.

When the platen 36 nears the end of its retraction stroke, the collar I22 on the control rod H1 is lifted by the platen arm l2l, shifting the servo-motor control valve member I04 to its neutral position, and placing the flow-control member of the variable delivery pump llll in its neutral or zero delivery position. This brings the platen 36 to a halt at the top of its retraction stroke.

It will be understood that I desire to'comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In combination with a hydraulic motor having a reciprocable ram, means forming with said motora ram-advancing circuit and a ram-retracting circuit for selectively operating said ram upon advance and retraction strokes respectively, a platen connected to said ram, a clamping motor mounted on said platen and movable therewith, a stationary auxiliary cylinder, a tubular plunger reciprocable in said auxiliary cylinder and connected to said clamping motor, a two-way valveoperative in one position to entrap fluid within said clamping motor; and auxiliary cylinderand in another position torelease fluid therefrom, pilot motor means for shifting said valve, means responsive to the admission of pressure fluid to said ram-retracting circuit for admittingpressure fluid to said pilot motor means to shift said valve into its fluid-releasing position,

and means adapted concomitantly into the initiation of advancing stroke ofsaid ram to admit pressure fluid oppositely to said pilot motor means for shifting said valve to its fluid-entrapping position.

2. In combination with a hydraulic motor hav- I 'in'g a reciprocable ram, means forming with said motor a ram-advancing circuit and aram-retracting circuit for selectively operating said ram upon advanceand retraction strokes respectively, .a platen connected to said ram, a clamping motor mounted on said platen and movable therewith, a

- clamping motor for selectively entrapping fluid therein and releasing fluid therefrom, a servomotor for reversing said pump, a source of pressure fluid connected to said servo-motor, a pilot valve for controlling the distribution of pressure fluid to said servomotor, and means responsive tothe admission of pressure fluid to said servomotor in reversing said pump to deliver pressure fluid to the ram-advancing circuit for shifting said first-mentioned valve to its fluid-entrapping' position prior to the engagement of the workpiece by said clamping member.

4. In combination with a hydraulic motor having a reciprocable ram, means forming with said motor a ram-advancing circuit and a ram-restationary auxiliary cylinder, a tubular plunger reciprocable in said auxiliary cylinder and connected to said clamping motor, a reversiblev variable delivery pump associated with a pilot pump and connected to said circuits so as to be adapted to selectively deliver pressure fluid to either of said circuits, a two-way valve operable by fluid pressure from said pilot pump to entrap fluid within said clamping motor and auxiliary cylin der, and means responsive to the reversal of said tracting circuit for selectively operating said ram upon advance and retraction strokes respectively, a platen connected to said ram, a clamping motor mounted on said platen and movable therewith, a fluid operable valve connected to said clamping motor and shiftable by pressure fluid selectively into one of two diiierent positions for releasing fluid from or entrapping fluid in said clamping motor, an auxiliary cylinder, a tubular plunger connecting said clamping motor with said auxiliary cylinder, and means adapted concomitantly with the initiation of the supply of pressure fluid to said ram-advancing circuit to cause shifting movement of said valve to its fluidentrapping position.

5. In combination with.- a hydraulic motor having a ram adapted to reciprocate in a main cylinder, means forming with said motor'a ramadvancing circuit and a ram-retracting circuit for selectively operating said ram upon advance and retraction strokes respectively, a platen connected to said ram, a clamping motor mounted on said platen and movable therewith, a two-way valve movable by pressure fluid selectively into one of two diiIerent positions to entrap fluid in or releasefluid from said clamping motor, means adapted at the beginning of the advancing stroke of said mm to supply pressure fluid to said valve I to shift the same into fluid-entrapping position,

WALTER ERNST. 

